Systems and methods for detection and removal of shadows in an image

ABSTRACT

In accordance with embodiments of the present disclosure, an information handling system may include a processor and a non-transitory computer-readable medium embodying a program of instructions. The program of instructions may be configured to, when read and executed by the processor, receive a visible-light image from a visible-light sensor, receive an infrared image from an active infrared sensor, and compare the visible-light image to the infrared image to determine shadow regions of the visible-light image having shadows.

TECHNICAL FIELD

The present disclosure relates in general to information handlingsystems, and more particularly, to video and/or still image capture andremoval of shadows from an image.

BACKGROUND

As the value and use of information continues to increase, individualsand businesses seek additional ways to process and store information.One option available to users is information handling systems. Aninformation handling system generally processes, compiles, stores,and/or communicates information or data for business, personal, or otherpurposes thereby allowing users to take advantage of the value of theinformation. Because technology and information handling needs andrequirements vary between different users or applications, informationhandling systems may also vary regarding what information is handled,how the information is handled, how much information is processed,stored, or communicated, and how quickly and efficiently the informationmay be processed, stored, or communicated. The variations in informationhandling systems allow for information handling systems to be general orconfigured for a specific user or specific use such as financialtransaction processing, airline reservations, enterprise data storage,or global communications. In addition, information handling systems mayinclude a variety of hardware and software components that may beconfigured to process, store, and communicate information and mayinclude one or more computer systems, data storage systems, andnetworking systems.

Information handling systems include cameras for capturing images,whether videos or still images. Such images may be used in manyapplications, including teleconferencing applications or simplycapturing images for entertainment, documentation, business, or otherpurposes.

In many image capture scenarios, the presence of strong shadows isundesirable and degrades the quality of the image. If such images aretaken of written material, such shadows may reduce legibility orreadability of content. Such shadows may be present in numerousscenarios, including when subjects are under uneven lighting conditionsor when capturing images outdoors in bright sunlight.

While some existing techniques may be used to reduce shadowing, suchtechniques may have shortcomings. For example, exposure levels inhigh-dynamic range (HDR) may be over-exposed or under-exposed and notset properly in shadow areas.

SUMMARY

In accordance with the teachings of the present disclosure, one or moredisadvantages and problems associated with reduction of shadows inimages may be reduced or eliminated.

In accordance with embodiments of the present disclosure, an informationhandling system may include a processor and a non-transitorycomputer-readable medium embodying a program of instructions. Theprogram of instructions may be configured to, when read and executed bythe processor, receive a visible-light image from a visible-lightsensor, receive an infrared image from an active infrared sensor, andcompare the visible-light image to the infrared image to determineshadow regions of the visible-light image having shadows.

In accordance with these and other embodiments of the presentdisclosure, a method may include receiving a visible-light image from avisible-light sensor, receiving an infrared image from an activeinfrared sensor, and comparing the visible-light image to the infraredimage to determine shadow regions of the visible-light image havingshadows.

In accordance with these and other embodiments of the presentdisclosure, an article of manufacture may include a non-transitorycomputer readable medium and computer-executable instructions carried onthe non-transitory computer readable medium, the instructions readableby a processor. The instructions, when read and executed, may cause theprocessor to receive a visible-light image from a visible-light sensor,receive an infrared image from an active infrared sensor, and comparethe visible-light image to the infrared image to determine shadowregions of the visible-light image having shadows.

Technical advantages of the present disclosure may be readily apparentto one skilled in the art from the figures, description and claimsincluded herein. The objects and advantages of the embodiments will berealized and achieved at least by the elements, features, andcombinations particularly pointed out in the claims.

It is to be understood that both the foregoing general description andthe following detailed description are examples and explanatory and arenot restrictive of the claims set forth in this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present embodiments and advantagesthereof may be acquired by referring to the following description takenin conjunction with the accompanying drawings, in which like referencenumbers indicate like features, and wherein:

FIG. 1 illustrates a block diagram of an example image capture system,in accordance with embodiments of the present disclosure;

FIG. 2 illustrates an example camera having multiple sensors, inaccordance with embodiments of the present disclosure;

FIGS. 3A-3C illustrate example images captured by sensors of the examplecamera depicted in FIG. 2, in accordance with embodiments of the presentdisclosure; and

FIG. 4 illustrates a flow chart of an example method for detection andremoval of shadows in an image, in accordance with embodiments of thepresent disclosure.

DETAILED DESCRIPTION

Preferred embodiments and their advantages are best understood byreference to FIGS. 1-4, wherein like numbers are used to indicate likeand corresponding parts.

For the purposes of this disclosure, an information handling system mayinclude any instrumentality or aggregate of instrumentalities operableto compute, classify, process, transmit, receive, retrieve, originate,switch, store, display, manifest, detect, record, reproduce, handle, orutilize any form of information, intelligence, or data for business,scientific, control, entertainment, or other purposes. For example, aninformation handling system may be a personal computer, a PDA, aconsumer electronic device, a network storage device, or any othersuitable device and may vary in size, shape, performance, functionality,and price. The information handling system may include memory, one ormore processing resources such as a central processing unit (CPU) orhardware or software control logic. Additional components of theinformation handling system may include one or more storage devices, oneor more communications ports for communicating with external devices aswell as various input and output (I/O) devices, such as a keyboard, amouse, and a video display. The information handling system may alsoinclude one or more buses operable to transmit communication between thevarious hardware components.

For the purposes of this disclosure, computer-readable media may includeany instrumentality or aggregation of instrumentalities that may retaindata and/or instructions for a period of time. Computer-readable mediamay include, without limitation, storage media such as a direct accessstorage device (e.g., a hard disk drive or floppy disk), a sequentialaccess storage device (e.g., a tape disk drive), compact disk, CD-ROM,DVD, random access memory (RAM), read-only memory (ROM), electricallyerasable programmable read-only memory (EEPROM), and/or flash memory; aswell as communications media such as wires, optical fibers, microwaves,radio waves, and other electromagnetic and/or optical carriers; and/orany combination of the foregoing.

For the purposes of this disclosure, information handling resources maybroadly refer to any component system, device or apparatus of aninformation handling system, including without limitation processors,service processors, basic input/output systems, buses, memories, I/Odevices and/or interfaces, storage resources, network interfaces,motherboards, and/or any other components and/or elements of aninformation handling system.

FIG. 1 illustrates a block diagram of an example image capture systemcomprising an information handling system 102, in accordance withembodiments of the present disclosure. In certain embodiments,information handling system 102 may comprise a personal computer (e.g.,a desktop computer or a portable computer). In these and otherembodiments, information handling system 102 may comprise a mobiledevice (e.g., smart phone, a tablet computing device, a handheldcomputing device, a personal digital assistant, or any other device thatmay be readily transported on a person of a user of such mobile device).In these and other embodiments, information handling system 102 maycomprise a Voice over Internet Protocol (VoIP) phone (e.g., apurpose-built hardware device that appears much like an ordinarylandline telephone). In these and other embodiments, informationhandling system 102 may comprise a video camera assembly. In these andother embodiments, information handling system 102 may comprise a stillcamera assembly.

As depicted in FIG. 1, information handling system 102 may include aprocessor 103, a memory 104 communicatively coupled to processor 103, astorage resource 110 communicatively coupled to processor 103, and auser interface 114 communicatively coupled to processor 103.

Processor 103 may include any system, device, or apparatus configured tointerpret and/or execute program instructions and/or process data, andmay include, without limitation, a microprocessor, microcontroller,digital signal processor (DSP), application specific integrated circuit(ASIC), or any other digital or analog circuitry configured to interpretand/or execute program instructions and/or process data. In someembodiments, processor 103 may interpret and/or execute programinstructions and/or process data stored in its memory 104, storageresource 110, and/or another component of information handling system102.

Memory 104 may be communicatively coupled to its associated processor103 and may include any system, device, or apparatus configured toretain program instructions and/or data for a period of time (e.g.,computer-readable media). Memory 104 may include random access memory(RAM), electrically erasable programmable read-only memory (EEPROM), aPCMCIA card, flash memory, magnetic storage, opto-magnetic storage, orany suitable selection and/or array of volatile or non-volatile memorythat retains data after power to its associated information handlingsystem 102 is turned off.

Each storage resource 110 may include a system, device, or apparatusconfigured to store data. A storage resource 110 may include one or morehard disk drives, magnetic tape libraries, optical disk drives,magneto-optical disk drives, solid state storage drives, compact diskdrives, compact disk arrays, disk array controllers, and/or any othersystems, apparatuses or devices configured to store data. In certainembodiments, storage resource 110 may include one or more storageenclosures configured to hold and/or power one or more of such devices.In the embodiments represented by FIG. 1, storage resource 110 mayreside within its associated information handling system 102. However,in other embodiments, storage resource 110 may reside external to itsassociated information handling system 102 (e.g., may be coupled toinformation handling system 102 via a network).

As shown in FIG. 1, a storage resource 110 may have stored thereon animaging application 112. Imaging application 112 may comprise a programof instructions which a processor 103 may read and execute to processimages captured by camera 120 to reduce or eliminate undesired shadowsfrom a visible light image captured by a visual light sensor of camera120, as described in greater detail below. When executed, activeportions of imaging application 112 may be loaded from storage resource110 into memory 104 for execution by processor 103. Although imagingapplication 112 is depicted in FIG. 1 as being locally stored to astorage resource 110 of an information handling system 102, in someembodiments, imaging application 112 may be stored externally orremotely from an information handling system 102 and accessible to suchinformation handling system 102 via a network, and loaded by processor103 from such network (e.g., such imaging application 112 may be astreaming application).

User interface 114 may comprise any instrumentality or aggregation ofinstrumentalities by which a participant subject 122 may interact withinformation handling system 102. For example, user interface 114 maypermit a user to input data and/or instructions into informationhandling system 102 (e.g., via a keypad, keyboard, touch screen,microphone, camera, and/or other data input device), and/or otherwisemanipulate information handling system 102 and its associatedcomponents. User interface 114 may also permit information handlingsystem 102 to communicate data to a participant 122 (e.g., via a displaydevice, speaker, and/or other data output device). As shown in FIG. 1,user interface 114 may include one or more of a display 116, microphone118, camera 120, and speaker 124.

A display 116 may comprise any suitable system, device, or apparatusconfigured to display human-perceptible graphical data and/oralphanumeric data to a participant 122. For example, in someembodiments, display 116 may comprise a liquid crystal display.

A microphone 118 may comprise any system, device, or apparatusconfigured to convert sound incident at microphone 118 to an electricalsignal that may be processed by processor 103. In some embodiments,microphone 118 may include a capacitive microphone (e.g., anelectrostatic microphone, a condenser microphone, an electretmicrophone, a microelectromechanical systems (MEMs) microphone, etc.)wherein such sound is converted to an electrical signal using adiaphragm or membrane having an electrical capacitance that varies asbased on sonic vibrations received at the diaphragm or membrane.

A camera 120 may comprise any system, device, or apparatus configured torecord images (moving or still) into one or more electrical signals thatmay be processed by processor 103. In some embodiments, camera 120 maycomprise a multiple-sensor camera configured to capture multiple typesof images, such as multiple-sensor camera 120 depicted in FIG. 2 anddescribed in greater detail below. In operation, camera 120 may captureimages of a subject 122, which may be a person (including, withoutlimitation, a user of information handling system 102), animal, or otherobject.

A speaker 124 may comprise any system, device, or apparatus configuredto produce sound in response to electrical audio signal input. In someembodiments, a speaker 124 may comprise a dynamic loudspeaker, whichemploys a lightweight diaphragm mechanically coupled to a rigid framevia a flexible suspension that constrains a voice coil to move axiallythrough a cylindrical magnetic gap such that when an electrical signalis applied to the voice coil, a magnetic field is created by theelectric current in the voice coil, making it a variable electromagnet.The coil and the driver's magnetic system interact, generating amechanical force that causes the coil (and thus, the attached cone) tomove back and forth, thereby reproducing sound under the control of theapplied electrical signal coming from the amplifier.

In addition to processor 103, memory 104, storage resource 110, and userinterface 114, information handling system 102 may include one or moreother information handling resources. Such an information handlingresource may include any component system, device or apparatus of aninformation handling system, including without limitation, a processor,bus, memory, I/O device and/or interface, storage resource (e.g., harddisk drives), network interface, electro-mechanical device (e.g., fan),display, power supply, and/or any portion thereof. An informationhandling resource may comprise any suitable package or form factor,including without limitation an integrated circuit package or a printedcircuit board having mounted thereon one or more integrated circuits.

FIG. 2 illustrates an example camera 120 having multiple sensors, inaccordance with embodiments of the present disclosure. As shown in FIG.2, camera 120 may include a visible light sensor 202, an active infraredsensor 204, an infrared source 206, a depth sensor 208, and a lightsource 210.

Visible light sensor 202 may comprise any system, device, or apparatusconfigured to sense electromagnetic energy in the visible spectrum(e.g., from approximately 400 nanometers in wavelength to approximately700 nanometers in wavelength) and based on the electromagnetic energysensed, capture a visible-light image having a plurality of pixelsrepresentative of the visible spectrum electromagnetic energy sensedrelative to each pixel, such as visible-light image 302 depicted in FIG.3A. Such visible-light image 302 may be black and white or color.Devices similar to visible light sensor 202 are often simply referred toas “cameras.”

Active infrared sensor 204 may comprise any system, device, or apparatusconfigured to sense electromagnetic energy in the non-visible infraredspectrum (e.g., greater than 700 nanometers in wavelength) and based onthe electromagnetic energy sensed, capture an infrared image having aplurality of pixels representative of the infrared spectrumelectromagnetic energy sensed relative to each pixel, such as infraredimage 304 depicted in FIG. 3B. As its name implies, active infraredsensor 204 senses infrared energy reflected from a subject 122originating from an active source 206 of infrared energy. Such infraredsource 206 may comprise any system, device, or apparatus located inclose proximity to infrared sensor 204 which emits infrared radiation(e.g., an infrared lamp for converting electrical energy intoelectromagnetic radiation in the infrared spectrum).

Depth sensor 208 may comprise any system, device, or apparatusconfigured to resolve distance based on the known speed of light,measuring a time-of-flight of a light signal between light source 210and subject 122 for each pixel of the image, and based on the distancesensed, capture a depth image having a plurality of pixelsrepresentative of the distance sensed relative to each pixel, such asdepth image 306 depicted in FIG. 3C. Light source 210 may comprise anysystem, device, or apparatus located in close proximity to depth sensor208 which emits electromagnetic radiation (e.g., visible light ornon-visible radiation). In some embodiments, depth sensor 208 maycomprise a time-of-flight camera. In other embodiments, depth sensor 208may comprise a structured light camera. In yet other embodiments, depthsensor 208 may comprise a stereo camera comprising at least two sensorsand an optional light source.

Although the foregoing contemplates a separate active infrared sensor204 and depth sensor 208, in some embodiments, depth sensor 208 andlight source 210 may also be capable of capturing two-dimensionalinfrared images, thus allowing depth sensor 208 to serve thefunctionality of infrared sensor 204 as well.

In operation, imaging application 112 may receive as inputs avisible-light image 302, an infrared image 304, and a depth image 306,and based thereon, identify potentially unwanted shadows present in thevisible-light image 302 (e.g., shadow 308 present in visible-light image302) and characterize such shadows in order to remove or reduce suchshadows. In other words, for each visible-light image 302 captured, acorresponding (e.g., substantially contemporaneous) infrared image 304and a corresponding (e.g., substantially contemporaneous) depth image306 are also captured. Because active source 206 may have the effect ofilluminating subject 122 like a flashlight from the point of view ofcamera 120, infrared sensor 204 may not “see” shadows resulting fromvisible light sources in the environment of subject 122. Thus, a trulydark material may typically appear dark in both the visible-light image302 and the corresponding infrared image 304, and because a shadow mayonly appear dark in the visible-light image 302, the visible-light image302 and its corresponding infrared image 304 may be compared to detectpixel regions in the visible-light image 302 that are dark (e.g., belowa pre-determined brightness threshold) but have corresponding pixelregions in the infrared image 304 that are not similarly dark. Anexample of this approach is described in greater detail with respect toFIG. 4, below.

FIG. 4 illustrates a flow chart of an example method 400 for detectionand removal of shadows in an image, in accordance with embodiments ofthe present disclosure. According to some embodiments, method 400 maybegin at step 402. As noted above, teachings of the present disclosuremay be implemented in a variety of configurations of informationhandling system 102. As such, the preferred initialization point formethod 400 and the order of the steps comprising method 400 may dependon the implementation chosen.

At step 402, imaging application 112 may initialize each value of a datastructure referred to herein as a shadow mask to zero. Such shadow maskmay include a plurality of values, each value corresponding to a pixelof a visible-light image 302.

At step 404, imaging application 112 may segment the visible-light image302 into dark regions and non-dark regions. For example, imagingapplication 112 may use an image segmentation algorithm andpre-determined thresholds for brightness and/or colors that areconsidered “dark.” As a result, regions of visible-light image 302, suchas shadow 308, may be identified as a dark region while the remainder ofthe visible-light image 302 may be identified as possessing non-darkregions. In some embodiments, imaging application 112 may also use depthimage 306 to automatically classify background pixels (e.g., thosepixels outside the infrared sensing range of infrared sensor 204 and thedepth sensing range of depth sensor 208 corresponding to black pixels ofdepth image 306 of FIG. 3C) as non-dark regions. Such automaticclassification of background pixels as being in non-dark regions mayreduce required image processing resources in cases in which it would bebeneficial to remove shadows in foreground objects, but such shadows canbe tolerated in background objects (e.g., portrait shots).

At step 406, imaging application 112 may compare each dark region of thevisible-light image 302 to its corresponding region of the infraredimage 304. At step 408, based on the comparisons, imaging application112 may determine if each corresponding region of the infrared image 304is also dark. Such determination may be made according to any standard,such as whether a corresponding region of the infrared image 304 has atleast a predetermined number and/or concentration of pixels in thecorresponding region of the infrared image 304 that fall below apredetermined brightness threshold for the region to be considered adark region. For each dark region of visible-light image 302 having acorresponding region of infrared image 304 determined to be dark, method400 may proceed to step 410. Otherwise, for each dark region ofvisible-light image 302 having a corresponding region of infrared image304 determined to not be dark, method 400 may proceed to step 412.

At step 410, in response to a dark region of visible-light image 302having a corresponding region of infrared image 304 determined not to bedark, meaning that such dark region is a shadow region, imagingapplication 112 may assign each value in the shadow mask for pixels inthe shadow region a value corresponding to a depth value associated withsuch pixel in depth image 306. Typically, a depth camera may assigns avalue of zero to the closest object of an image, and the values increaseas the depth of the objects increase. However, in the presentdisclosure, the depth value assigned in step 410 may employ an inverseof such approach, in which background objects have a depth value ofzero, and with increasing values or objects closer to camera 120. Aftercompletion of step 410, method 400 may end.

At step 412, in response to a dark region of visible-light image 302having a corresponding region of infrared image 304 determined to bedark, meaning that such dark region is not a shadow region, imagingapplication 112 may assign each value in the shadow mask for pixels notin a shadow region a value of zero, indicating that such pixels are notin shadow regions. After completion of step 412, method 400 may end.

Although FIG. 4 discloses a particular number of steps to be taken withrespect to method 400, method 400 may be executed with greater or fewersteps than those depicted in FIG. 4. In addition, although FIG. 4discloses a certain order of steps to be taken with respect to method400, the steps comprising method 400 may be completed in any suitableorder.

Method 400 may be implemented using one or more information handlingsystems 102, components thereof, and/or any other system operable toimplement method 400. In certain embodiments, method 400 may beimplemented partially or fully in software and/or firmware embodied incomputer-readable media.

After the shadow mask for the visible-light image 302 is createdaccording to method 400, data of the shadow mask may be processed byimaging application 112 to remove or reduce shadows and render acorrected visible-light image 302 with the shadows removed or reduced.The scope of such shadow reduction based on a shadow mask is outside thescope of this disclosure, although one example technique may involveusing the values present in the shadow mask, which are representative ofa depth of each pixel in shadow regions, to characterize a surface shapeof subjects in the shadow regions in order to edit the visible-lightimage 302 to reduce or eliminate the appearance of shadows.

It is to be understood that the image analysis approaches discussedabove are not limited to the embodiments disclosed above. For example,in analyzing visible-light image 302 to determine dark regions, imagingapplication 112 may in some embodiments process certain channels of acolor image (e.g., a luminance channel). As another example, in someembodiments, sensors 202, 204, and 208 may not be positioned in theexact location and may have differences in resolution and otherparameters, such that the systems and methods described above may needto account for differences in the corresponding images 302, 304, and306. Thus, imaging application 112 may in some embodiments compensatefor such differences by adjusting a pixel map to account for offsetsbetween sensors and other sensor parameters. Alternatively, imagingapplication 112 may use pixel information from infrared image 304 anddepth image 306 to detect shadow pixels, and then “grow” to neighboringpixels in the visible-light image 302 that exhibit the same color and/orbrightness characteristics as the known shadow pixels.

This disclosure encompasses all changes, substitutions, variations,alterations, and modifications to the exemplary embodiments herein thata person having ordinary skill in the art would comprehend. Similarly,where appropriate, the appended claims encompass all changes,substitutions, variations, alterations, and modifications to theexemplary embodiments herein that a person having ordinary skill in theart would comprehend. Moreover, reference in the appended claims to anapparatus or system or a component of an apparatus or system beingadapted to, arranged to, capable of, configured to, enabled to, operableto, or operative to perform a particular function encompasses thatapparatus, system, or component, whether or not it or that particularfunction is activated, turned on, or unlocked, as long as thatapparatus, system, or component is so adapted, arranged, capable,configured, enabled, operable, or operative.

All examples and conditional language recited herein are intended forpedagogical objects to aid the reader in understanding the invention andthe concepts contributed by the inventor to furthering the art, and areconstrued as being without limitation to such specifically recitedexamples and conditions. Although embodiments of the present inventionshave been described in detail, it should be understood that variouschanges, substitutions, and alterations could be made hereto withoutdeparting from the spirit and scope of the disclosure.

1. An information handling system, comprising: a processor; and anon-transitory computer-readable medium embodying a program ofinstructions, the program of instructions configured to, when read andexecuted by the processor: receive a visible-light image from avisible-light sensor; receive an infrared image from an active infraredsensor; and compare the visible-light image to the infrared image todetermine shadow regions of the visible-light image having shadows. 2.The information handling system of claim 1, wherein comparing thevisible-light image to the infrared image comprises: segmenting thevisible-light image into dark regions and non-dark regions; comparingeach dark region of the visible-light image to a corresponding region ofthe infrared image; and for each dark region of the visible-light image,determining the dark region to be shadow region if the correspondingregion of the infrared image is not dark.
 3. The information handlingsystem of claim 2, the program of instructions further configured to:receive a depth image from a depth sensor; and for each shadow region,assign each value in a shadow mask associated with the visible-lightimage for each pixel of the visible-light image in the shadow region, avalue corresponding to a depth value associated with such pixel in thedepth image.
 4. The information handling system of claim 3, the programof instructions further configured to assign for each value of theshadow mask for each pixel not in any shadow region, a value indicatingsuch pixel is not in a shadow region.
 5. The information handling systemof claim 2, the program of instructions further configured to: receive adepth image from a depth sensor; and analyze the depth image forbackground regions of the visible-light image; wherein segmenting thevisible-light image into dark regions and non-dark regions comprisessegmenting the background regions into non-dark regions.
 6. Theinformation handling system of claim 2, the program of instructionsfurther configured to reduce an appearance of shadows in thevisible-light image based on the shadow mask.
 7. The informationhandling system of claim 1, the program of instructions furtherconfigured to: receive a depth image from a depth sensor; and comparethe visible-light image to the infrared image and the depth image todetermine shadow regions of the visible-light image having shadows.
 8. Amethod, comprising: receiving a visible-light image from a visible-lightsensor; receiving an infrared image from an active infrared sensor; andcomparing the visible-light image to the infrared image to determineshadow regions of the visible-light image having shadows.
 9. The methodof claim 8, wherein comparing the visible-light image to the infraredimage comprises: segmenting the visible-light image into dark regionsand non-dark regions; comparing each dark region of the visible-lightimage to a corresponding region of the infrared image; and for each darkregion of the visible-light image, determining the dark region to beshadow region if the corresponding region of the infrared image is notdark.
 10. The method of claim 9, further comprising: receiving a depthimage from a depth sensor; and for each shadow region, assigning eachvalue in a shadow mask associated with the visible-light image for eachpixel of the visible-light image in the shadow region, a valuecorresponding to a depth value associated with such pixel in the depthimage.
 11. The method of claim 10, further comprising assigning for eachvalue of the shadow mask for each pixel not in any shadow region, avalue indicating such pixel is not in a shadow region.
 12. The method ofclaim 9, further comprising: receiving a depth image from a depthsensor; and analyzing the depth image for background regions of thevisible-light image; wherein segmenting the visible-light image intodark regions and non-dark regions comprises segmenting the backgroundregions into non-dark regions.
 13. The method of claim 9, furthercomprising reducing an appearance of shadows in the visible-light imagebased on the shadow mask.
 14. The method of claim 8, further comprising:receiving a depth image from a depth sensor; and comparing thevisible-light image to the infrared image and the depth image todetermine shadow regions of the visible-light image having shadows. 15.An article of manufacture comprising: a non-transitory computer readablemedium; and computer-executable instructions carried on thenon-transitory computer readable medium, the instructions readable by aprocessor, the instructions, when read and executed, for causing theprocessor to: receive a visible-light image from a visible-light sensor;receive an infrared image from an active infrared sensor; and comparethe visible-light image to the infrared image to determine shadowregions of the visible-light image having shadows.
 16. The article ofclaim 15, wherein comparing the visible-light image to the infraredimage comprises: segmenting the visible-light image into dark regionsand non-dark regions; comparing each dark region of the visible-lightimage to a corresponding region of the infrared image; and for each darkregion of the visible-light image, determining the dark region to beshadow region if the corresponding region of the infrared image is notdark.
 17. The article of claim 16, the instructions for further causingthe processor to: receive a depth image from a depth sensor; and foreach shadow region, assign each value in a shadow mask associated withthe visible-light image for each pixel of the visible-light image in theshadow region, a value corresponding to a depth value associated withsuch pixel in the depth image.
 18. The article of claim 17, theinstructions for further causing the processor to assign for each valueof the shadow mask for each pixel not in any shadow region, a valueindicating such pixel is not in a shadow region.
 19. The article ofclaim 16, the instructions for further causing the processor to: receivea depth image from a depth sensor; and analyze the depth image forbackground regions of the visible-light image; wherein segmenting thevisible-light image into dark regions and non-dark regions comprisessegmenting the background regions into non-dark regions.
 20. The articleof claim 16, the instructions for further causing the processor toreduce an appearance of shadows in the visible-light image based on theshadow mask.
 21. The article of claim 15, the instructions for furthercausing the processor to: receive a depth image from a depth sensor; andcompare the visible-light image to the infrared image and the depthimage to determine shadow regions of the visible-light image havingshadows.